In the traditional information retrieval, a query consists of keywords and ID numbers combined with logical connectives such as AND and OR. Character-string matching and statistical methods have been basic technologies there. For the interaction with the user, keywords/words and phrases characterizing several subsets of the set of solution candidates are found by statistical methods, and presented as hints to let the user select some of them to augment the query. Related art has been disclosed in the following documents:
Yoshihiko Hayashi, Yoshitsugu Obashi, “Technical Trend of Retrieval Service on WWW”, Information Processing, Vol. 39, No. 9, 1998, and
Sumio Fujita, “Approach to Retrieving/Classifying Information by utilizing Natural Language Processing”, Information Processing, Vol. 40, No. 4, 1999.